This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Human CDC5 (hCDC5) is an important regulator of G2/M in mammalian cells. It is rapidly phosphorylated upon serum stimulation of cells, and we propose that phosphorylation regulates hCDC5 function. We seek to employ mass spectrometry to map the phosphorylation sites in hCDC5. We will use these data to make phosphospecific mutants and test their role in hCDC5 function.